The General Packet Radio Service (GPRS) standard provides a compatibility standard for cellular mobile telecommunications systems. The GPRS standard ensures that a mobile station (MS) operating in a GPRS system can obtain communication services when operating in a system manufactured according to the standard. To ensure compatibility, radio system parameters and data transfer procedures are specified by the standard, including protocols governing digital control messages and bearer traffic that are exchanged over an air interface.
In order for a mobile station (MS) to access a GPRS communication system, the MS must first obtain operating information about the system when the MS activates or roams into the system. To facilitate the MS's acquisition of the information, the GPRS standards, in particular 3GPP TS 05.02 (Third Generation Partnership Project Technical Specification 05.02), version 8.10.0, Release 1999, provides for a broadcast, by a Radio Access Network (RAN), of system operating parameters in a Packet Broadcast Control Channel (PBCCH).
Among the types of information that the GPRS standards require that the RAN provide to the MS is Packet System Information (PSI), which information is broadcast in PSI messages. 3GPP TS 05.02 Section 6.3.2.4 requires that the PSI messages be broadcast in specific multiframes and, within each multiframe, within specific blocks of the multiframe allocated to the PBCCH. Typically, there are 12 blocks in a multiframe in a GPRS communication system. The standards further specify three types of PSI messages, that is, a PSI1 message(s), a PSI message(s) that is transmitted with a high repetition rate, and a PSI message(s) that is transmitted with a low repetition rate.
In order to assure that an MS accessing a GPRS system can obtain the requisite PSI messages, the standards further provide for repeated broadcast of the PSI messages. The repeated broadcast is governed by two parameters, a PSI1 repeat period parameter (i.e., PSI1_REPEAT_PERIOD) and a parameter indicating a number of blocks per multiframe allocated to the PBCCH (i.e., BS_PBCCH_BLKS).
The PSI1 repeat period parameter (PSI1_REPEAT_PERIOD) corresponds to how often a PSI1 message is repeated, in terms of a number of multiframes. That is, from another perspective, the PSI1 repeat period parameter corresponds to a number of multiframes in a repeat period. For example, a PSI1 repeat period equal to ‘3’ indicates that a PSI1 message is repeated once every three multiframes, or that there are three multiframes in a repeat period.
The PBCCH block parameter (BS_PBCCH_BLKS) corresponds to a number of PBCCH blocks of each multiframe allocated to the PBCCH. For example, a PBCCH block parameter equal to ‘4’ indicates that the four blocks (typically out of 12) of each multiframe in a repeat period are allocated to the PBCCH. If the PSI1 repeat period parameter is set to ‘3’ and the PBCCH block parameter is set to ‘4,’ then twelve (12) blocks in total would be allocated to the PBCCH in each PSI1 repeat period. While the standards provide for the broadcast of the PSI1 repeat period parameter and the PBCCH block parameter, the standards do not disclose how to determine these parameters.
The standards dictate that all PSI1 messages and high repetition rate PSI messages be repeated during each PSI1 repeat period. The low repetition rate PSI messages are then conveyed during a PSI1 repeat period only when extra PBCCH blocks are available. In accordance with the standards, the first one or two blocks allocated to the PBCCH in each repeat period are allocated to the PSI1 message(s). The succeeding PBCCH blocks of the multiframes of the repeat period are then allocated to high repetition rate PSI messages. Any remaining PBCCH blocks of the multiframes of the repeat period that are not consumed by the PSI1 message(s) and the high repetition rate PSI messages are then allocated to the low repetition rate PSI messages. As a result, when an insufficient number of PBCCH blocks are allocated per repeat period to permit a conveyance of all of the PSI1, high repetition rate PSI, and low repetition rate PSI messages, an MS seeking to access a system may have to listen to several PSI1 repeat periods before the MS is able to acquire all of the low repetition rate PSI messages. In the meanwhile, the MS is acquiring redundant PSI1 messages and high repetition rate PSI messages and is being delayed in accessing the communication system.
In order to minimize a likelihood that an MS seeking to access a system may have to listen to several PSI1 repeat periods, it may be desirable to provide a larger PBCCH block parameter (more PBCCH blocks per multiframe) or a longer PSI1 repeat period (more multiframes per repeat period). However, when an MS acquires the PBCCH in the midst of a PSI1 repeat period, the MS must wait until the beginning of the next repeat period, that is, for the next PSI1 message, before the MS may begin acquiring the PSI messages. Thus a longer PSI1 repeat period may result in a longer access time for an MS, that is, a longer wait for an MS seeking to access a network. Furthermore, a longer PSI1 repeat period may result in wasted PBCCH blocks if there are not sufficient low repetition rate PSI messages to fill all remaining PBCCH blocks after the blocks are first allocated to the PSI1 message(s) and the high repetition rate PSI messages. On the other hand, provision of a larger PBCCH block parameter (more PBCCH blocks per multiframe) reduces the number of blocks in a multiframe allocated to non-PBCCH channels and carrying non-PSI data. In addition, provision of a larger PBCCH block parameter may waste multiframe blocks if there are not sufficient low repetition rate PSI messages to fill all remaining PBCCH blocks after the blocks are first allocated to the PSI1 message(s) and the high repetition rate PSI messages.
For example, FIG. 1 is a block diagram of an exemplary PSI1 repeat period 100. As depicted in FIG. 1, PSI1 repeat period 100 comprises three (3) multiframes 102-104, that is, PSI1_REPEAT_PERIOD=3. Each multiframe 102-104 comprises 12 blocks, and four blocks 106 of each multiframe 102-104 are assigned to a PBCCH 108, that is, BS_PBCCH_BLKS=4. The blocks allocated in each multiframe to the PBCCH need not be contiguous, for example, FIG. 1 depicts blocks 1, 4, 7, and 10 of each multiframe allocated to PBCCH 108. As further depicted by FIG. 1, four PSI messages are conveyed over PBCCH 108. The four PSI messages comprise a PSI1 message that must be conveyed twice during the first multiframe 102 of each PSI repeat period 100, a PSI2 message that is a high repetition rate (HR) PSI message and that also must be conveyed during each PSI repeat period 100, and a PSI3 message and a PSI3bis message that are low repetition rate (LR) messages and that are conveyed during a PSI repeat period 100 only when blocks 106 of PBCCH 108 remain available.
The PSI1 message depicted in FIG. 1 has a single instance and is assigned a first block 106 of PBCCH 108, which block corresponds to a first block, that is, block 1, of a first multiframe 102 of the three multiframes 102-104. The PSI1 message is also repeated in another block 106 of PBCCH 108, that is, block 7 of the first multiframe 102 of the three multiframes 102-104. The PSI2 message depicted in FIG. 1 has two instances, that is, PSI2—1 and PSI2—2, that are assigned to two available blocks 106 of PBCCH 108 that are not assigned to the PSI1 message. As depicted in FIG. 1, the two instances of the PSI2 message are assigned to blocks 4 and 10 of multiframe 102. The PSI3 and PSI3bis messages depicted in FIG. 1 have one instance and six (6) instances, respectively, which instances are assigned successive, available blocks 106 in PBCCH 108 after the PBCCH blocks assigned to the instances of the PSI1 and PSI2 messages.
Due to a sub-optimal determination of a duration of PSI repeat period 100 and of a number of blocks 106 per multiframe 102-104 allocated to PBCCH 108, an instance PSI3—1 of LR message PSI3 is assigned to multiple blocks 106 of PBCCH 108 in PSI repeat period 100, that is, to block 1 of a second multiframe 103 and to block 10 of a third multiframe 104. Such redundancy is inefficient as it wastes a data block. However, if fewer blocks 106, for example three (3) blocks, in each multiframe 102-104 are assigned to PBCCH 108, then PSI repeat period would be unable to accommodate all of the instances of the LR PSI messages. In such an event, the instances not included in the depicted PSI repeat period would then be assigned to the first available blocks 106 of PBCCH 108 in the next PSI repeat period after the allocation of PBCCH blocks to the instances of the PSI1 message and the HR PSI messages, that is, the PSI2 message. However, an MS acquiring the PSI messages when then have to wait for two PSI repeat periods in order to obtain the system information conveyed by the PSI messages. Also an allocation of fewer blocks per multiframe to the PBCCH and a longer repeat period can result in a longer wait for an MS acquiring the PSI messages when the MS begins acquiring the PBCCH in the middle of a PSI repeat period, but an allocation of more blocks per multiframe to the PBCCH reduces an amount of non-PSI information that may be conveyed per multiframe.
Therefore, a need exists for a method and an apparatus that optimizes a determination of the PBCCH block and the PSI1 repeat period parameters.